The need to remove sulfur from sulfur-contaminated catalysts, such as reforming catalysts, and from sulfur-contaminated reactor walls (e.g., iron sulfide scale) is well known. A sulfur-contaminated reactor system, will continue to produce sulfur compounds (such as H.sub.2 S) under reducing conditions for an extended period of time, sometimes lasting several days. These sulfur compounds can decrease catalyst performance, including activity, stability and/or selectivity.
The problems associated with this sulfur contamination have been addressed in numerous patents and in a variety of ways. For example, U.S. Pat. No. 4,507,397 to Buss teaches a method of regenerating catalysts in sulfur contaminated vessels, piping, etc, where iron sulfide scale has built up during processing. The method uses an in-situ oxidation step using a dry oxygen-containing gas to form oxides of sulfur. Alternatively, U.S. Pat. No. 3,732,123 to Stolfa teaches the descaling of heater tubes by alternately subjecting the deposited scale to oxidation and reduction techniques. Preferably, more than one series of alternating oxidation and reduction steps are used, the later ones being carried out at temperatures from about 1050.degree. F. to about 1250.degree. F. Recently, several patents have issued on methods for cleaning reactor systems prior to using a highly sulfur-sensitive catalysts, such as Pt L-zeolite. For example, U.S. Pat. No. 4,940,532 to Peer et al. discloses a method of preparing a previously used reactor for use with a sulfur-sensitive catalyst. Peer uses a sacrificial particle bed of Pt/Sn and manganese oxide to remove contaminants, such as sulfur, from a conversion system. Subsequently, the sacrificial particle bed is replaced by a sulfur-sensitive catalyst, such as a reforming catalyst selective for dehydrocyclization. Also, U.S. Pat. No. 5,035,792 to Foutsitzis et al. discloses that a hydrocarbon solvent, preferably an aromatic solvent, can be utilized to purge contaminants, such as sulfur, from a conversion system. This process fills the system with an aromatic solvent, such as toluene, to purge sulfur compounds from the reactor walls. It is taught that gases which "are inert to reaction with the solvent or contaminant," such as nitrogen or hydrogen, may be combined with the solvent (see Col. 4, lines 63-9). Additional contaminant-removal steps such as oxidation, reduction, and contaminant removal with a sacrificial particulate bed are also disclosed. This solvent purge is intended to avoid deactivation of a subsequently loaded contaminant sensitive catalyst, such as a reforming catalyst selective for dehydrocyclization. The need to recover the activity of catalysts poisoned by feed sulfur is also well known. For example, U.S. Pat. No. 4,155,836 to Collins et al. discloses that Pt halogen-containing reforming catalysts can be deactivated by feeds containing high levels of sulfur (at least 10 ppm) and water (at least 50 ppm). The resulting contaminated catalysts may have their activity restored by discontinuing the hydrocarbon feed and passing hydrogen and halogen over the catalyst to reduce its sulfur concentration. The typical feed to this process generally has a relatively high sulfur level (between about 1 and 5 ppm). Therefore, the impact of sulfur contamination due to reaction of contaminated process equipment is not observed or discussed.
Additionally, Heyse et al., (WO 92/15653) teach coating portions of reforming reactors with metallic coats to prevent carbonization, coking and metal dusting. A preferred coating for this use is a tin coating. Also, U.S. Ser. No. 000,285 to Heyse et al. teach applying metallic coats to sulfur-contaminated reactors as a method of treating and desulfiding sulfided steels. These patent applications do not address the problem of sulfur upsets, such as that associated with inadvertent sulfur contamination of hydrocarbon feeds.
Indeed, none of the above-described patents disclose a process for quickly and easily removing sulfur contaminants from process equipment, especially from a metal-coated reactor system. Nor do they teach or suggest the advantages associated with the various embodiments of the present invention as described below.